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Quantum-enhanced Raman microscopy
Quantum-enhanced Raman microscopy is a chemical imaging technique that uses squeezed light to reduce noise below the shot-noise limit, improving Raman microscope sensitivity without extra sample power.
Quantum-to-classical transition
The quantum-to-classical transition is the problem of how classical behavior with definite properties emerges from quantum mechanics, its leading account being environment-induced decoherence, first proposed by H. Dieter Zeh.
Quark
A quark is a fundamental particle carrying fractional electric charge that combines with other quarks to form hadrons such as protons and neutrons; six flavors are known.
Quark coalescence
Quark coalescence, or quark recombination, is a model of hadron formation in heavy-ion collisions where hadrons are built directly from quarks already present in the deconfined quark-gluon plasma rather than by fragmentation.
Quark model
The quark model, proposed by Murray Gell-Mann and George Zweig in 1964, classifies hadrons as bound states of quarks: mesons of a quark and antiquark, baryons of three quarks.
Quark star
A quark star is a hypothetical compact star made of deconfined quark matter rather than neutrons, sitting alongside neutron stars and black holes as an endpoint of stellar evolution; none has been confirmed.
Quark–gluon plasma
The quark–gluon plasma, or quark soup, is a state of matter with free quarks and gluons that filled the early universe and is now made by colliding heavy ions.
Quark–gluon plasma in small systems
Quark–gluon plasma in small systems is the study of whether QGP forms in proton, deuteron, and light-ion collisions, once used as QGP-free controls, with flow and jet-quenching evidence since about 2010.
Quark–hadron phase transition
The quark–hadron phase transition is the change in quantum chromodynamics between confined hadronic matter and the deconfined quark–gluon plasma, studied in the early universe and heavy-ion collisions.
QuarkNet
QuarkNet is a United States professional development and outreach program, founded in 1999, that partners high school teachers and students with particle physicists on experiments at CERN and Fermilab.
Quarkonium
Quarkonium (plural quarkonia) is a bound state of a heavy quark and its own antiquark, the analog of positronium; its suppression in heavy-ion collisions probes the quark-gluon plasma.
Quarkyonic matter
Quarkyonic matter is a conjectured phase of quantum chromodynamics at high baryon density and low temperature, in which quarks are the relevant degrees of freedom but remain confined, developed mainly by Larry McLerran.
Quart
The quart is a unit of volume equal to one quarter of a gallon, with a U.S. liquid quart of about 0.946 liter, a larger dry quart, and a British Imperial quart of 1.136 liters.
Quarter-wave plate
A quarter-wave plate, or λ/4 plate, is an optical element made of birefringent material that delays one polarization component by a quarter wavelength, converting linear into circular or elliptically polarized light.
Quartic function
A quartic function is a polynomial function of degree four, solved generally by Lodovico Ferrari's method in 1540. It is the highest degree solvable by radicals.
Quartile
A quartile is one of three cut points dividing ordered data into four equal groups: Q1 at the 25th percentile, Q2 the median, and Q3 the 75th.
Quartz
Quartz, also known as rock crystal, is a crystalline mineral of silicon dioxide, abundant in igneous, metamorphic, and sedimentary rocks, famous for its purple amethyst variety.
Quartz clock
A quartz clock keeps time using the vibration of a piezoelectric quartz crystal, replaced pendulums as national standards in 1929, and now times billions of wristwatches.
Quartz crystal microbalance with dissipation
Quartz crystal microbalance with dissipation (QCM-D) is a surface-sensitive acoustic technique that measures frequency and dissipation shifts to study adsorption and viscoelastic properties of polymer, biomolecular, and cell layers.
Quartzite
Quartzite, also known as metaquartzite, is a hard, quartz-rich metamorphic rock formed when sandstone or chert recrystallizes under regional or thermal metamorphism; the name also covers some well-cemented sandstone.
Quasar
A quasar, short for quasi-stellar radio source, is an extremely luminous galactic center powered by a supermassive black hole consuming gas, outshining its host galaxy.
Quasar clustering
Quasar clustering is the statistical excess of quasar pairs at given separations, measured to show how these active supermassive black holes trace the large-scale structure of the universe.
Quasar Hubble diagram
The quasar Hubble diagram is a plot of distance against redshift for quasars, using their UV and X-ray luminosity relation to test cosmology at redshifts beyond Type Ia supernovae.
Quasar luminosity function
The quasar luminosity function is the comoving number density of quasars per unit luminosity, whose evolution with redshift traces the history of accretion onto supermassive black holes.
Quasar quartet
The quasar quartet is the first known system of four quasars in close proximity, discovered in 2015 with the Keck I Telescope in Hawaii and announced in Science.
Quasi-Biennial Oscillation
The quasi-biennial oscillation (QBO) is a quasi-periodic reversal of equatorial stratospheric winds averaging about 28 months, first detected in 1960 and among the most predictable atmospheric cycles.
Quasi-elastic neutron scattering
Quasi-elastic neutron scattering (QENS) is a neutron spectroscopy technique that measures broadening of the elastic line from stochastic diffusive motions, revealing diffusion coefficients and molecular motion geometry.
Quasi-experiment
A quasi-experiment, also called a quasi-experimental design, is a study design for estimating causal effects without random assignment, using repeated measurements or a comparison group instead.
Quasi-Fermi level
A quasi-Fermi level, also called Imref, is a fictitious Fermi level assigned separately to electrons and holes in a semiconductor under illumination or bias, where equilibrium is broken.
Quasi-fission
Quasi-fission is a fission-like outcome of a heavy-ion collision in which two touching nuclei re-separate before forming an equilibrated compound nucleus, strongly suppressing superheavy element synthesis.